There are an estimated 10,000-15,000 deaths in the United States each year due to sudden infant death syndrome (SIDS), making it the most frequent cause of death in the first year of life. Many hypotheses have been formulated to explain its etiology. Most of the easily recognized post-mortem abnormalities in the victims are in the lungs and they have usually been interpreted as evidence of a sudden catastrophic event in an otherwise normal infant. Years of speculation about the nature of the catastrophic event have been unfruitful because the easily recognized post-mortem abnormalities give few clues to the dynamic events surrounding the deaths.
The term "apnoea" is often used in conjunction with SIDS as a symptom as well as a cause. Apnoea may be defined as a pause in the infant's breathing equal to or exceeding six seconds. Short periods of apnoea during sleep are normal during infancy while prolonged periods are abnormal. In 1972 Steinschneider (Pediatrics 50:646-654, 1972) reported that several SIDS victims had prolonged periods of apnoea during sleep before death.
In an attempt to combat SIDS, monitoring systems have been proposed in the past which react to any period of apnoea in the sleeping infant. Although some of the indications may be false alarms due to normal periods of apnoea by the infant, in any event, the parents or attending nurses are alerted by the monitors whenever the infant stops breathing, even for a short period.
The prior art monitors, however, suffer from a disadvantage in that they usually involve placing electrodes on the infant with leads extending to the monitoring equipment. These electrodes and leads are a source of discomfort to the infant and inhibit normal sleep. Moreover, the electrodes themselves often cause skin irritation. Another problem is the fact that such prior art systems exhibit failures with no detectable electrical fault and, accordingly, are believed to be unreliable.
The use of infrared energy to detect if an infant has stopped breathing has been suggested in the prior art. The exhalations of the infant include large quantities of carbon dioxide. Carbon dioxide is absorbent to the long wave infrared radiation. The detector detects the difference in the infrared radiation due to the absorption incident to the exhalations of the infant. The resulting signal is applied to a suitable alarm circuit to indicate an interruption of the exhalation exceeding a predetermined time interval.
A non-contacting apnoea detector is disclosed in U.S. Pat. No. 4,350,166. However, the detector relies on infrared radiation from the infant itself, which peaks at 9.6 microns; whereas carbon dioxide is absorbed at 15 microns. This militates substantially against the effectiveness of the prior art device.
The monitoring system of the apnoea monitor of the present invention is simple in its construction, yet it is extremely reliable, and it is capable of detecting apnoea in the infant without any primary or secondary electrical hook-ups to the child itself. As explained briefly above, the apnoea monitoring system of the invention collects the exhaled breath of the infant in an area in which infrared energy is emitted from an infrared source and, through infrared absorption, measures the quantity of carbon dioxide present in the breath. So long as the carbon dioxide is present, the child is breathing. Should apnoea occur and the child stops breathing, the carbon dioxide will disappear and an infrared detector will respond to the resulting rise in the infrared intensity to cause an alarm to be triggered. This permits the attending nurse or parents to take immediate life saving action.
It is accordingly an objective of the present invention to provide an improved simple and inexpensive apnoea monitoring system which detects and continuously monitors actual infant breathing, without any physical contact with the infant itself. The system of the invention is advantageous in that it is highly reliable, it is not subject to failure, and it does not involve complex and inconvenient wire hook-ups which are uncomfortable and disturbing to the infant.